I just encountered, that my webpage dropped 7 pages low on google in just 1 week. How is that even remotely possible? I didn't change anything regarding metatags, descriptions, site structure, whatsoever.

And still it's displayed on page 7 when searching for the most used keyword (which I sorted out with google analytics)

Does anyone have an idea how that can even happen in such short time?

Interesting note; The viewer count didn't change too much during the whole time. Also the pagerank didn't change - still 5

I know there are many possibilities, and my page droppend and gained places every time over the past year, but this drop is so enormous I figured there had to be something really wrong here.
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Florian PeschkaAug 24 '10 at 12:18

As mentioned, their ranking algorithms can change, other sites don't stop competing to top spots, etc. You're likely to always go up and down unless you're the master authority for your keywords at which point it would be harder to knock you off the top.

It's very common for a site's rankings to go up and down, but 7 pages does sound a bit excessive. (I'm assuming you definitely mean 7 pages i.e. ~70 places, not just 7 places). It's also very unlikely that 70 other sites will have suddenly made huge improvements to their SEO.

The reasons I have seen for most sites is a hacking. Check your pages, particularly your page source, to make sure it's what should be displayed. Log into Google Webmaster Tools to see if there are any messages about possible hackings or spam on your site.

Another reason, although unlikely to make a huge difference in one week, it that Googlebot is having trouble accessing the site. This could be a server problem or maybe even a misconfigured robots.txt. Check your site on DownForEveryoneOrJustMe.com and WebPageTest.org, and check the robots.txt section in GWT.